EPR oximetry is an emerging technology that can make repeated and accurate measurements of pO2 from the same site in viable systems, using particulate oxygen-sensitive paramagnetic materials. This revised competing renewal aims to bring this potentially very productive technique to a level of maturity where its special capabilities can be applied to the numerous areas of research that will benefit significantly from the availability of such measurements, and to develop the technology to facilitate its adoption by other scientists for experimental and potential clinical uses. It will especially focus on making it feasible to use these capabilities to advance progress in the understanding and therapy of cancer. The progress achieved in the first six years of the PPG has verified the usefulness and also the need for such an approach, as we have both achieved significant new experimental results and delineated some critical aspects of the technology that need further development. The rationale for carrying out these studies in a PPG is based on the need to have an integrated and synergistic set of studies that together provide the range of capabilities needed to develop fully this very promising technique. The PPG involves collaborative efforts at three different sites. It is based at Dartmouth where there is a leading NIH supported center for the broad development of in vivo EPR spectroscopy, which provides very strong and economical instrumental support for the proposed studies. The project at Dartmouth also has appropriate expertise and experience to carry out several inter-related aspects of the research, including making comparisons of EPR oximetry with complimentary methods for the direct and indirect measurements of oxygen in tissues and in preparing the technique for applications in the clinic. The project at the U. Of Illinois provides unique capabilities in the development and characterization of paramagnetic materials, especially chars, for use both as oximetric sensors per se and to understand the characteristics that control the properties of oximetric particulate materials. The project at the U. Of Louvain provides unique expertise in the coating of paramagnetic materials and in pharmaceutical aspects to facilitate the use of EPR oximetry in experimental animals and, eventually, in patients. The key personnel involved in the PPG have an established record of effective productive collaboration and are highly committed to carrying out the crucial next steps to make this technology fully effective and available for use by other investigators.